According to the World Health Organization, six Indian cities feature among the top ten with the worst polluted air.

India’s capital New Delhi was the survey’s ninth worst city, with an annual average PM2.5 measurement of 122, WHO said on Thursday.

Central Indian cities of Gwalior, Allahabad, Patna and Raipur followed Iranian city of Zabol as the top five cities with the dirtiest air. Ludhiana and Delhi were also in the top ten.

Two Chinese cities Xingtai and Baoding were ranked seventh and eight respectively. WHO compared a total of 795 cities in 67 countries for levels of small and fine particulate matter (PM10 and PM2.5) during the five-year period, 2008-2013.

The report showed that while rich countries improved the state of their air over the same period, poorer nations struggled.